1. Field of the Invention
The present invention relates to an optical disc drive and a control method thereof, and more particularly, to an optical disc drive for stably driving many kinds of high density optical discs and a control method thereof.
2. Related Art
An optical disc drive is a device for projecting a laser beam on a spiral track formed on a recording layer surface of an optical disc to record and reproduce information. The recording of information is performed by generating a pit in the recording track, and the reproduction of information is performed by projecting a laser beam on the track formed with the pits and analyzing variation of the quantity of the laser beam reflected from the recording pits.
The laser beam projected from a light source, such as semiconductor laser diode (LD), is focused on the recording track by the operation of optical components, such as an objective lens, a prism, and the like to generate a light spot of a diameter less than few μm. In order to record and reproduce information of the optical disc, the light spot must be continuously formed on the very narrow track.
However, since the optical disc has a bending of about 200 μm on the recording layer surface and about 50 μm track deflection, the track moves with a large amplitude as the optical disc rotates. Due to these reasons, in order to focus the light spot on a target track and to track the recording track, the objective lens must be controlled using two servo-controls such as a focus servo-control and a tracking servo-control.
The focus servo-control is to control the objective lens to move in the normal direction with respect to the surface of the optical disc such that a light spot having a predetermined size is formed on the track of the optical disc so that the size of the light spot is controlled. In contrast, the tracking servo-control is to control the objective lens to move in the radial direction of the optical disc such that the light spot is formed along the center of the track so that the position of the light spot is controlled.
Optical components within the optical disc drive used to control the objective lens are typically part of an optical pickup or a pickup module. Such an optical pickup or pickup module contains two actuators for driving the objective lens, a sensor for detecting the position of the light spot, and a carriage for housing the optical components, and a linear actuator for driving the carriage in the radial direction of the optical disc. Also included in the optical disc drive are a digital signal processor, a servo-controller, and a motor.
A blue-ray disc (hereinafter referred to a ‘BD’) as a high density optical disc has a numerical aperture of 0.85 which is relatively higher than those of an HD DVD, a DVD, and a CD. Thus, since the pickup module of the optical disc drive approaches more closely the surface of the BD for the recording/reproducing/erasing of information in comparison to a case of other optical discs, a stable control is required to prevent the objective lens of the pickup module colliding against the surface of the BD.
For example, when a kind of an optical disc in which information is recorded/reproduced/erased is wrongly determined by the optical disc drive, the information is recorded/reproduced/erased by an unexpected recording/reproducing strategy instead of a recording/reproducing strategy adequate for a corresponding optical disc. Due to this common occurrence, the possibility of generating an abnormal control signal different from a normal control signal (a tracking error signal or a focus error signal) generated when using the adequate recording/reproducing/erasing strategy is very high. Therefore, the control of the pickup module by the abnormal tracking error signal or the focus error signal cannot be reliable. Accordingly, this problem must be addressed and prevented in view of collision between the pickup module and the optical disc.